(a) Field of the Invention
The present invention relates to iron-base alloys which have a high elastic limit after appropriate thermal treatment and are resistant to corrosion by seawater, marine sludge, salt spray and brackish waters.
(b) Prior Art
For the manufacture of certain articles intended to be used for long periods in an underwater environment, for example articles forming part of submarine teletransmission cables, it is necessary to use stainless steels or alloys which are extremely resistant to corrosion by seawater and the sludge deposited on the sea-bed on which the cable rests.
Certain parts of such submarine cables are subjected, while they are being laid on the sea bottom or while they are being brought up for checking or maintenance work, to extremely large stresses which depend on the depth of immersion and on the condition of the sea at the time when the cable is laid or lifted. One kind of cable part which is liable to be subjected to such stresses is the underwater repeater which may need to be lifted several years after it has been laid. Although the seawater-resistant stainless steels which are conventionally employed for such purposes are resistant to corrosion during long periods of immersion, they have an inadequate elastic limit for the parts to be able to withstand the considerable stress which can be caused by lifting operations after immersion for several years.
No alloys are at present known which resist corrosion by seawater and marine sludge as satisfactorily as stainless steels, such as the steel marketed under the trademark URANUS 50 by Creusot-Loire, and which, at the same time, have a high elastic limit after quenching and ageing treatment, for example an elastic limit of more than 600 Newtons/mm.sup.2.